How to write lease for unmarried couples?

[B R]

85% of the showings of our 4br SFH have been to unmarried couples, where the male makes most of the income.

How do you treat this situation in your leases? Do they both need to earn 3X the rent in income in order to qualify? What if one half of the couple qualifies and the other doesn't?

I can see these boyfriend/girlfriend things going badly just like any other roommate situation, with one tenant moving out and leaving the weaker one behind.

Thoughts?